There has been proposed a printer that forms an image electrophotographically, in which a process cartridge is removably mounted to an apparatus body. The process cartridge includes a developing cartridge having a developing roller and a photosensitive cartridge to which the developing cartridge is removably mounted and which has a photosensitive drum.
The process cartridge is pressed in a constant direction for positioning when it is mounted to the apparatus body. In addition, there has been also proposed a printer which brings a developing roller into contact with a photosensitive drum when forming an image, and separates the developing roller from the photosensitive drum when an image is not being forming.
For example, JP-A-2003-215876 describes a related image forming apparatus which positions a process cartridge on the apparatus body by pressing a bearing of a photosensitive drum downward by a twist coil spring such that the bearing is pressing against a butting surface of a guide groove.
In the related image forming apparatus, a switching means for separating the developing roller from the photosensitive drum is provided. The switching means separates the developing roller from the photosensitive drum by pressing-up a rib provided on the developing unit using a separating plate.